Sintered Compact Magnesium Oxide Target for Sputtering, and Method for Producing Same

ABSTRACT

A sintered compact magnesium oxide target for sputtering having a purity of 99.99 wt % or higher excluding C, a density of 3.57 g/cm 3  or higher, and a whiteness of 60% or less. In order to uniformly deposit a magnesium oxide film, a magnesium oxide target having a higher purity and a higher density is being demanded. An object of this invention is to provide a target capable of realizing the above, and a method for producing such a target. While a magnesium oxide sintered compact sputtering target is produced by hot-pressing a raw material powder, there is a problem in that color shading occurs in roughly φ60 (within a circle having a diameter of 60 mm) at the center part of the target. Conventionally, no particularly attention was given to this problem. However, in recent years, it has become necessary to investigate and resolve this problem in order to improve the deposition quality.

TECHNICAL FIELD

The present invention relates to a magnesium oxide target for use informing a magnesium oxide layer for magnetic recording mediums ofmagnetic disk devices or tunneling magnetoresistance (TMR) elements andother electronic devices, and to the method of producing such amagnesium oxide target; and particularly relates to a sintered compactmagnesium oxide target for sputtering of high purity and high densityand which is free of color shading that occurs at the center of thetarget, and to the method of producing such a sintered compact magnesiumoxide target for sputtering.

BACKGROUND

In recent years, pursuant to the downsizing and higher recording densityof magnetic disks, research and development of magnetic recordingmediums are being conducted, and in particular Co-based magnetic layersand under-layers have been improved variously.

Meanwhile, the recording density of hard disks has been increasingrapidly year by year, and it is considered that current surface densityof 600 Gbit/in² will reach 1 Tbit/in² in the future. When the recordingdensity reaches 1 Tbit/in², the recording bit size will be less than 10nm and, in such a case, it is anticipated that the superparamagnetismcaused by thermal fluctuation will become a problem. The currently usedmagnetic recording medium structure such as a structure with increasedmagnetic crystalline anisotropy obtained by adding Pt to a Co—Cr-basedalloy will become insufficient.

This is because magnetic particles that behave with stableferromagnetism at a size of 10 nm or less require even greater magneticcrystalline anisotropy.

Due to the foregoing reason, a Fe—Pt phase having an L1₀ structure isattracting attention as a structure for use in an ultra high densityrecording medium. Since the Fe—Pt phase having an L1₀ structurepossesses high magnetic crystalline anisotropy in addition to yieldingsuperior corrosion resistance and oxidation resistance, it is expectedto be a structure that can be suitably applied to a magnetic recordingmedium.

When using a Fe—Pt layer as a structure for use in an ultra high densityrecording medium, it is demanded to develop a technology of dispersingordered Fe—Pt magnetic particles regulated in the same direction with adensity as high as possible in a magnetically isolated state. While itis necessary to control the crystal orientation in order to providemagnetic anisotropy to the Fe—Pt thin film, this can be easily performedby selecting a single crystal substrate. In order to vertically align aneasy axis, it has been reported that a magnesium oxide film is suitableas the under-layer of the Fe—Pt layer.

In addition, it is also known that a magnesium oxide film can besuitably used as the insulating layer, i.e., tunnel barrier of a TMRelement that is used in a magnetic head (for hard disks) or an MRAM.While the foregoing magnesium oxide film has been conventionally formedvia the vacuum deposition method, in recent years the sputtering methodis being used to produce magnesium oxide films from the perspective ofsimplification of the production process and facilitation of theproduction of large screens.

There are the following publications as conventional technology.

Patent Document 1 describes a magnesium oxide target made from amagnesium oxide sintered compact having a magnesium oxide purity of99.9% or higher than a relative density of 99% or higher, wherein themagnesium oxide target has a fine structure in which the average grainsize is 60 μm or less and round pores having an average grain size of 2μm or less exist in the crystal grains, and is compatible up to asputter deposition rate of 1000 Å/min or more. This technique is basedon a method of adding fine magnesium oxide powder having an averagegrain size of 100 nm or less to high purity magnesium oxide powder andmixing and compacting the powders, and subjecting the obtained compactto primary sintering and secondary sintering.

Patent Document 2 relates to a magnesium oxide target made from amagnesium oxide sintered compact having a relative density of 99% orhigher and capable of achieving a deposition rate of 500 Å/min or higherin sputter deposition performed in an Ar atmosphere or Ar—O₂ mixedatmosphere, and proposes compacting high purity magnesium oxide powderhaving an average grain size of 0.1 to 2 μm based on CIP at a pressureof 3 t/cm² or higher, and sintering the obtained compact.

Patent Document 3 describes a magnesium oxide target made from amagnesium oxide sintered compact having a magnesium oxide purity of99.9% or higher and a relative density of 99.0% or higher, andcompatible up to a sputter deposition rate of 600 Å/min or more. Thistechnique is based on a method of adding electromelted magnesium oxidepowder and fine magnesium oxide powder having an average grain size of100 nm or less to high purity magnesium oxide powder and mixing andcompacting the powders, and subjecting the obtained compact to primarysintering and secondary sintering. Patent Document 3 describes that amagnesium oxide film having favorable orientation, crystallinity andfilm properties can be deposited via the sputtering method at a highdeposition rate.

Patent Document 4 describes a target having MgO as its main component,as well as a method for producing such a target, and proposes dispersingLa particles, Y particles and Sc particles in a target having MgO as itsmain component for use as a protective film of a dielectric layer of anAc-type PDP in order to achieve a low discharge voltage, sputteringresistance during discharge, quick responsiveness to discharge, andinsulation properties.

Patent Document 5 proposes, in a target having MgO as its maincomponent, dispersing LaB₆ particles in the MgO matrix, performingreduction treatment in a reduced gas atmosphere prior to sintering, andperforming primary sintering and secondary sintering at a predeterminedtemperature in order to improve the strength, fracture toughness value,and resistance to thermal shock.

Patent Document 6 prescribes the relative density and the averagecrystal grain size to be 0.5 to 100 μm in a target having MgO as itsmain component, and dispersing the rare earth elements of Sc, Y, La, Ce,Gd, Yb, and Nd in the MgO matrix.

Patent Document 7 proposes sintering a MgO green compact based on thespark plasma sintering method in order to produce a high densitysintered compact.

Patent Document 8 and Patent Document 9 describe methods of obtaining aMgO sintered compact with numerous (111) planes aligned based onuniaxial pressure sintering and having an ultimate density of 3.568g/cm³ so as to achieve favorable mechanical property and thermalconductivity, and reduction in contamination of the atmosphere caused bythe generation of gas, and propose subjecting MgO raw material powderhaving a grain size of 1 μm or less to uniaxial pressure sintering, andsubsequently performing heat treatment in an oxygen atmosphere at atemperature of 1273 K or higher. In the foregoing case, MgO is used asthe raw material powder, and the method of increasing the density islimited to the sintering conditions.

Patent Document 10 proposes a target for depositing a MgO film in alarge size and uniform manner. In addition to prescribing the averagecrystal grain size, the density, the deflective strength, and the centerline average roughness of the target surface, Patent Document 10proposes causing the grain size of the raw material powder to be 1 μm orless, subjecting the raw material powder to granulation, sintering thegranulated raw material powder at a predetermined load and temperature,and finishing the surface of the target to achieve a center line averageroughness Ra of 1 μm or less. Incidentally, while not directly relatedto the present invention, foregoing Patent Document 1 to Patent Document6, Patent Document 8, and Patent Document 9 describe the evaluation ofthe “bending strength” of a target, and Patent Document 10 describes theevaluation of the “deflective strength” of a target.

CITATION LIST Patent Documents

-   Patent Document 1: JP-A-H10-130827-   Patent Document 2: JP-A-H10-130828-   Patent Document 3: JP-A-H10-158826-   Patent Document 4: JP-A-H10-237636-   Patent Document 5: JP-A-H11-6058-   Patent Document 6: JP-A-H11-335824-   Patent Document 7: JP-A-H11-139862-   Patent Document 8: JP-A-2009-173502-   Patent Document 9: WO2009/096384-   Patent Document 10: JP-A-2000-169956

SUMMARY OF THE INVENTION Problems to be Solved

In recent years, the use of a magnesium oxide film in recording mediumsof magnetic disk devices (hard disks) or tunneling magnetoresistance(TMR) elements and other electronic devices is being considered, but amagnesium oxide target having a higher purity and a higher density isbeing demanded in order to uniformly deposit a magnesium oxide film.Nevertheless, since expectations for higher purification anddensification are extremely high, it was conventionally difficult toproduce a magnesium oxide target capable of meeting the foregoingdemands. Thus, an object of this invention is to provide a targetcapable of realizing the above, and a method for producing such atarget.

Moreover, while a magnesium oxide sintered compact sputtering target isproduced by hot-pressing a raw material powder, there is a problem inthat color shading occurs in roughly φ60 (within a circle having adiameter of 60 mm) at the center part of the target. Conventionally, noparticularly attention was given to this problem. However, in recentyears, it has become necessary to investigate and resolve this problemin order to improve the deposition quality.

Means for Solving the Problems

In order to achieve the foregoing object, as a result of intense study,the present inventors discovered that a magnesium oxide target having ahigher purity and a higher density can be obtained with inexpensiveprocessing conditions in comparison to conventional methods based on theselection of raw material powders and the optimal setting of sinteringconditions. In addition, with respect to the occurrence of colorshading, the present inventors additionally discovered that it ispossible to produce a uniformly gray magnesium oxide target that is freeof color shading, and which comprises a moderate oxygen defect.

Based on the foregoing discovery, the following invention is provided.

1) A sintered compact magnesium oxide target for sputtering having apurity of 99.99 wt % or higher excluding C, a density of 3.57 g/cm³ orhigher, and a whiteness of 60% or less.

2) The sintered compact magnesium oxide target for sputtering accordingto 1) above, wherein the sintered compact magnesium oxide target forsputtering is produced by using a raw material obtained by adding MgCO₃in an amount of 5 wt % or more and less than 30 wt % to magnesium oxide(MgO).

3) The sintered compact magnesium oxide target for sputtering accordingto 1) or 2) above, wherein the whiteness is 55% or higher and 60% orless.

4) The sintered compact magnesium oxide target for sputtering accordingto any one of 1) to 3) above, wherein variation in the whiteness iswithin 5%.

5) A method for producing a sintered compact magnesium oxide target forsputtering which uses a raw material obtained by adding MgCO₃ in anamount of 5 wt % or more and less than 30 wt % to magnesium oxide (MgO),wherein raw material powders made of magnesium oxide (MgO) and MgCO₃having a purity of 99.99 wt % or higher excluding C and an average grainsize of 0.5 μm or less are mixed, and the mixed powders are hot pressedat a temperature of 1500° C. or less and an applied pressure of 300kgf/cm² or more to obtain a sintered compact magnesium oxide target forsputtering having a purity of 99.99 wt % or higher excluding C, and adensity of 3.57 g/cm³ or higher.

6) A method for producing the sintered compact magnesium oxide targetfor sputtering according to any one of 1) to 4) above which uses a rawmaterial obtained by adding MgCO₃ in an amount of 5 wt % or more andless than 30 wt % to magnesium oxide (MgO), wherein raw material powdersmade of magnesium oxide (MgO) and MgCO₃ having a purity of 99.99 wt % orhigher excluding C and an average grain size of 0.5 μm or less aremixed, and the mixed powders are hot pressed at a temperature of 1500°C. or less and an applied pressure of 300 kgf/cm² or more to obtain asintered compact magnesium oxide target for sputtering having a purityof 99.99 wt % or higher excluding C, and a density of 3.57 g/cm³ orhigher.

Effect of Invention

The present invention is effective in uniformly depositing a magnesiumoxide film, and specifically provides a high purity, high densitysintered compact magnesium oxide target that is free of color shadingand can be produced at a low cost by selecting the appropriate rawmaterial powders. It is also possible to obtain a high density targethaving a uniform composition. Moreover, the generation of particlesduring sputtering can be consequently inhibited. In addition, since itis possible to produce a sintered compact magnesium oxide targetcomprising a moderate oxygen defect, excessive oxygen is not generatedduring sputtering, and an effect of inhibiting oxidation of the adjacentdeposition layer (metal layer) is exhibited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the correlation of the additive amount ofmagnesium carbonate (MgCO₃) and the relative density of the sinteredcompact magnesium oxide target.

FIG. 2 is a diagram showing the correlation of the additive amount ofmagnesium carbonate (MgCO₃) and the whiteness of the sintered compactmagnesium oxide target.

DETAILED DESCRIPTION OF THE INVENTION

The sintered compact magnesium oxide target for sputtering of thepresent invention has a purity of 99.99 wt % or higher excluding C, adensity of 3.57 g/cm³ or higher, and a whiteness of 60% or less, and amajor feature of the present invention is that the sintered compactmagnesium oxide target for sputtering has a whiteness of 55% or higherand 60% or less.

This target can be realized by producing the target using a raw materialobtained by adding MgCO₃ in an amount of 5 wt % or more and less than 30wt % to magnesium oxide (MgO). Note that the whiteness was measuredusing the micro surface spectral color difference meter VSS400 (JIS Z8722, ASTM E 308) manufactured by Nippon Denshoku Industries. ThisHunter-type color difference meter was used to measure L: luminosity anda·b (hue·chroma), and the whiteness was obtained from the followingformula.

W (whiteness)=100−[(100−L)²+(a ² +b ²)]^(1/2)   Formula

Conventionally, magnesium oxide (MgO) was sintered, but sufficientdensity could not be obtained unless the sintering temperature was sethigh. The present invention can achieve a density of 3.57 g/cm³ or morewith a sintering temperature of 1500° C. or less as described below.This is a low temperature compared to conventional methods, and thus itis possible to reduce the production cost. In addition, the presentinvention can obtain a sintered compact magnesium oxide target forsputtering having a purity of 99.99% or higher excluding C.

As described above, it is even more advantageous to have an effect ofreducing the nodules and particles because reduction of the variation inwhiteness causes improvement in the uniformity of the sintered compact.Here, the variation in whiteness is preferably adjusted to be within 5%.

Upon producing the sintered compact magnesium oxide target forsputtering of the present invention, a MgCO₃ raw material in an amountof 5 wt % or more and less than 30 wt % is used. This raw material has apurity of 99.99 wt % or higher excluding C, and, after mixing the MgCO₃raw material powders having an average grain size of 0.5 μm or less, themixed powders are hot pressed at a temperature of 1500° C. or less andan applied pressure of 300 kgf/cm² or more to obtain a target having apurity of 99.99 wt % or higher excluding C, and a density of 3.57 g/cm³or higher. Note that magnesium carbonate (MgCO₃) is decomposed duringsintering (MgCO₃→MgO+CO₂).

EXAMPLES

The Examples are now explained. Note that these Examples merelyillustrate preferred representative examples, and it should be easy tounderstand that the present invention should not be limited to theseExamples. The technical concept of the present invention shall beinterpreted based on the overall descriptions of this specification andparticularly based on the scope of claims.

Example 1

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingMgCO₃ in an amount of 6.0 wt % and remainder being magnesium oxide (MgO)having a purity of 99.99 wt % or higher excluding C and an average grainsize of 0.5 μm or less was mixed. Note that the C content in this rawmaterial powder was 0.86 wt %.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.576 g/cm³ (relative density 99.74%) was obtained.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was gray, andthe target possessed optical transparency. Moreover, upon examining thewhiteness of the target, the whiteness was 58.6%. In addition, thevariation in whiteness was 3.9%. For this whiteness, the whiteness byHunter (Lab) was obtained by using the “micro surface spectral colordifference meter VSS400” manufactured by Nippon Denshoku Industries. Themeasuring range diameter in the foregoing case was 0.2 mmφ. Three pointswere randomly measured to obtain the average value and variation (σ)thereof. In the following Examples and Comparative Examples, thewhiteness was measured and the variation thereof was measured in asimilar manner.

TABLE 1 Additive Amount of MgCO₃ Sintered Variation C Content RawSintering Hold Pressing Compact Relative in in Raw Material TemperatureTime Pressure Density Density Optical Whiteness Whiteness Material (wt.%) (° C.) (Hours) (kgf/cm²) (g/cm³) (%) Color Transparency (%) (%) (wt.%) Comparative 0.0 1500 2 300 3.280 91.49 White No 91.3 1.4 0.00 Example1 Comparative 1.8 1500 2 300 3.482 97.11 White No 81.5 1.6 0.26 Example2 Comparative 3.0 1500 2 300 3.540 98.74 Light gray, Yes 72.2 10.5 0.43Example 3 spots Comparative 4.2 1500 2 300 3.568 99.53 Light gray Yes63.5 0.3 0.60 Example 4 Example 1 6.0 1500 2 300 3.576 99.74 Gray Yes58.6 3.9 0.86 Example 2 9.0 1500 2 300 3.576 99.75 Gray Yes 57.6 0.61.28 Example 3 12.0 1500 2 300 3.572 99.64 Gray Yes 55.6 3.2 1.71Example 4 15.0 1500 2 300 3.577 99.79 Gray Yes 56.6 1.1 2.14 Example 518.0 1500 2 300 3.571 99.62 Gray Yes 56.1 3.4 2.57 Comparative 30.0 15002 300 3.572 99.62 Gray, spots Yes 56.5 5.2 4.28 Example 5 Comparative48.0 1500 2 300 3.577 99.78 Gray, spots Yes 56.4 6.8 6.84 Example 6Comparative 60.0 1500 2 300 3.573 99.65 Gray, spots, Yes 56.6 8.1 8.55Example 7 cracks

Example 2

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingMgCO₃ in an amount of 9.0 wt % and remainder being magnesium oxide (MgO)having a purity of 99.99 wt % or higher excluding C and an average grainsize of 0.5 μm or less was mixed. Note that the C content in this rawmaterial powder was 1.28 wt %.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.576 g/cm³ (relative density 99.75%) was obtained.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was gray, andthe target possessed optical transparency. Moreover, upon examining thewhiteness of the target, the whiteness was 57.6%. In addition, thevariation in whiteness was 0.6%.

Example 3

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingMgCO₃ in an amount of 12.0 wt % and remainder being magnesium oxide(MgO) having a purity of 99.99 wt % or higher excluding C and an averagegrain size of 0.5 μm or less was mixed. Note that the C content in thisraw material powder was 1.71 wt %.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.572 g/cm³ (relative density 99.64%) was obtained.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was gray, andthe target possessed optical transparency. Moreover, upon examining thewhiteness of the target, the whiteness was 55.6%. In addition, thevariation in whiteness was 3.2%.

Example 4

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingMgCO₃ in an amount of 15.0 wt % and remainder being magnesium oxide(MgO) having a purity of 99.99 wt % or higher excluding C and an averagegrain size of 0.5 μm or less was mixed. Note that the C content in thisraw material powder was 2.14 wt %.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.577 g/cm³ (relative density 99.79%) was obtained.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was gray, andthe target possessed optical transparency. Moreover, upon examining thewhiteness of the target, the whiteness was 56.6%. In addition, thevariation in whiteness was 1.1%.

Example 5

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingMgCO₃ in an amount of 18.0 wt % and remainder being magnesium oxide(MgO) having a purity of 99.99 wt % or higher excluding C and an averagegrain size of 0.5 μm or less was mixed. Note that the C content in thisraw material powder was 2.57 wt %.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.571 g/cm³ (relative density 99.62%) was obtained.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was gray, andthe target possessed optical transparency. Moreover, upon examining thewhiteness of the target, the whiteness was 56.1%. In addition, thevariation in whiteness was 3.4%.

Comparative Example 1

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingmagnesium oxide (MgO) having a purity of 99.99 wt % or higher and anaverage grain size of 0.5 μm or less was used. Note that magnesiumcarbonate (MgCO₃) was not added to this raw material powder. C contentwas <10 ppm.

Subsequently, this raw material powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. The density of the obtained MgO sintered compact wasmeasured with the Archimedes method. Consequently, a density of 2.280g/cm³ (relative density 91.49%) was obtained. In comparison to theExamples, the density decreased significantly.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was white, andthe target did not possess optical transparency. Moreover, uponexamining the whiteness of the target, the whiteness was 91.3%. Inaddition, the variation in whiteness was 1.4%.

Comparative Example 2

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingmagnesium oxide (MgO) and magnesium carbonate (MgCO₃) in an amount of0.18 wt % having a purity of 99.99 wt % or higher excluding C and anaverage grain size of 0.5 μm or less was mixed. C content was 0.26 wt %.In the foregoing case, the amount of magnesium carbonate (MgCO₃) did notsatisfy the amount of the present invention.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.482 g/cm³ (relative density 97.11%) was obtained. In comparison tothe Examples, the density decreased significantly.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was white, andthe target did not possess optical transparency. Moreover, uponexamining the whiteness of the target, the whiteness was 81.5%. Inaddition, the variation in whiteness was 1.6%.

Comparative Example 3

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingmagnesium oxide (MgO) and magnesium carbonate (MgCO₃) in an amount of3.0 wt % having a purity of 99.99 wt % or higher excluding C and anaverage grain size of 0.5 μm or less was mixed. C content was 0.43 wt %.In the foregoing case, the amount of magnesium carbonate (MgCO₃) did notsatisfy the amount of the present invention.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.540 g/cm³ (relative density 98.74%) was obtained. In comparison tothe Examples, the density decreased.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was light graybut “spots” appeared on the surface. The target possessed opticaltransparency.

Moreover, upon examining the whiteness of the target, the whiteness was72.2%. In addition, the variation in whiteness was 10.5%.

Comparative Example 4

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingmagnesium oxide (MgO) and magnesium carbonate (MgCO₃) in an amount of4.2 wt % having a purity of 99.99 wt % or higher excluding C and anaverage grain size of 0.5 μm or less was mixed. C content was 0.60 wt %.In the foregoing case, the amount of magnesium carbonate (MgCO₃) did notsatisfy the amount of the present invention.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.568 g/cm³ (relative density 99.53%) was obtained. In comparison tothe Examples, the density decreased.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was lightgray, and the target possessed optical transparency. Moreover, uponexamining the whiteness of the target, the whiteness was 63.5%. Inaddition, the variation in whiteness was 0.3%.

Comparative Example 5

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingmagnesium oxide (MgO) and magnesium carbonate (MgCO₃) in an amount of30.0 wt % having a purity of 99.99 wt % or higher excluding C and anaverage grain size of 0.5 μm or less was mixed. C content was 4.3 wt %.In the foregoing case, the amount of magnesium carbonate (MgCO₃) exceedsthe amount of the present invention.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.572 g/cm³ (relative density 99.62%) was obtained, and the densitywas equivalent to the Examples.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was gray but“spots” appeared on the surface. This is considered to be a result of anincrease in the amount of magnesium carbonate (MgCO₃). Moreover, uponexamining the whiteness of the target, the whiteness was 56.5%. Inaddition, the variation in whiteness was 5.2%.

Comparative Example 6

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingmagnesium oxide (MgO) and magnesium carbonate (MgCO₃) in an amount of48.0 wt % having a purity of 99.99 wt % or higher excluding C and anaverage grain size of 0.5 μm or less was mixed. C content was 6.8 wt %.In the foregoing case, the amount of magnesium carbonate (MgCO₃) exceedsthe amount of the present invention.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.577 g/cm³ (relative density 99.78%) was obtained, and the densitywas equivalent to the Examples.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was gray but“spots” appeared on the surface. This is considered to be a result of anincrease in the amount of magnesium carbonate (MgCO₃). Moreover, uponexamining the whiteness of the target, the whiteness was 56.4%. Inaddition, the variation in whiteness was 6.8%.

Comparative Example 7

The sintered compact magnesium oxide target for sputtering was producedaccording to the following method. A raw material powder containingmagnesium oxide (MgO) and magnesium carbonate (MgCO₃) in an amount of60.0 wt % having a purity of 99.99 wt % or higher excluding C and anaverage grain size of 0.5 μm or less was mixed. C content was 8.55 wt %.In the foregoing case, the amount of magnesium carbonate (MgCO₃)considerably exceeds the amount of the present invention.

Subsequently, this mixed powder was hot pressed for 2 hours at atemperature of 1500° C. and an applied pressure of 300 kgf/cm² toproduce a magnesium oxide target having a purity of 99.99 wt % or higherexcluding C. Note that, since magnesium carbonate (MgCO₃) is decomposedduring sintering (MgCO₃→MgO+CO₂), magnesium carbonate (MgCO₃) does notexist in the sintered target. The density of the obtained MgO sinteredcompact was measured with the Archimedes method. Consequently, a densityof 3.573 g/cm³ (relative density 99.65%) was obtained, and the densitywas equivalent to the Examples.

The sintered compact produced as described above was subject to grindingand polishing to obtain a sintered compact magnesium oxide target forsputtering. Upon visually observing the target, the color was gray but“spots” appeared on the surface. Moreover, cracks were generated inaddition to the “spots”. This is considered to be a result of anincrease in the amount of magnesium carbonate (MgCO₃).

Moreover, upon examining the whiteness of the target, the whiteness was56.6%. In addition, the variation in whiteness was 8.1%.

As evident from the foregoing Examples and Comparative Examples, therelative density of the sintered compact magnesium oxide target of thepresent invention is affected by the additive amount of the magnesiumcarbonate (MgCO₃). A density of 3.57 g/cm³ (relative density of 99.5%)can be achieved by adding MgCO₃ in an amount of 5 wt % or more and lessthan 30 wt %. This is shown in FIG. 1.

Moreover, the whiteness of the sintered compact magnesium oxide targetof the present invention is affected by the additive amount of themagnesium carbonate (MgCO₃). The whiteness becomes 60% or less by addingMgCO₃ in an amount of 5 wt % or more and less than 30 wt %. This isshown in FIG. 2.

Accordingly, a target produced by using a raw material obtained byadding MgCO₃ in an amount of 5 wt % or more and less than 30 wt % to themagnesium oxide (MgO) has a high density, and is effective as a sinteredcompact magnesium oxide target for sputtering.

Moreover, as evident from the foregoing Examples and ComparativeExamples, it is more effective to adjust the variation in whiteness tobe within 5% since an effect of decreasing the cracks and nodules of thesintered compact can be obtained.

The present invention yields a superior effect of being able to obtain ahigh purity, high density sintered compact magnesium oxide target thatis free of color shading and can be produced at a low cost by selectingthe appropriate raw material powder. It is also possible to improve thecharacteristics of the deposition of magnesium oxide. Further, thegeneration of particles during sputtering can be consequently inhibited.In addition, since it is possible to produce a sintered compactmagnesium oxide target comprising a moderate oxygen defect, excessiveoxygen is not generated during sputtering, and an effect of inhibitingoxidation of the adjacent deposition layer (metal layer) is exhibited.

Accordingly, the magnesium oxide sintered compact sputtering target ofthe present invention is useful as a magnesium oxide sputtering targetfor use in forming a magnesium oxide layer for magnetic recordingmediums of magnetic disk devices or tunneling magnetoresistance (TMR)elements and other electronic devices.

1. A sintered compact magnesium oxide target for sputtering having apurity of 99.99 wt % or higher excluding C, a density of 3.57 g/cm³ orhigher, and a whiteness of 60% or less.
 2. The sintered compactmagnesium oxide target for sputtering according to claim 1, wherein thesintered compact magnesium oxide target for sputtering is produced byusing a raw material obtained by adding MgCO₃ in an amount of 5 wt % ormore and less than 30 wt % to magnesium oxide (MgO).
 3. The sinteredcompact magnesium oxide target for sputtering according to claim 2,wherein the whiteness is 55% or higher and 60% or less.
 4. The sinteredcompact magnesium oxide target for sputtering according to claim 3,wherein variation in the whiteness is within 5%.
 5. A method forproducing a sintered compact magnesium oxide target for sputtering whichuses a raw material obtained by adding MgCO₃ in an amount of 5 wt % ormore and less than 30 wt % to magnesium oxide (MgO), wherein rawmaterial powders made of magnesium oxide (MgO) and MgCO3 having a purityof 99.99 wt % or higher excluding C and an average grain size of 0.5 μmor less are mixed, and the mixed powders are hot pressed at atemperature of 1500° C. or less and an applied pressure of 300 kgf/cm²or more to obtain a sintered compact magnesium oxide target forsputtering having a purity of 99.99 wt % or higher excluding C, and adensity of 3.57 g/cm³ or higher.
 6. A method for producing the sinteredcompact magnesium oxide target for sputtering according to claim 1 whichuses a raw material obtained by adding MgCO₃ in an amount of 5 wt % ormore and less than 30 wt % to magnesium oxide (MgO), wherein rawmaterial powders made of magnesium oxide (MgO) and MgCO₃ having a purityof 99.99 wt % or higher excluding C and an average grain size of 0.5 μmor less are mixed, and the mixed powders are hot pressed at atemperature of 1500° C. or less and an applied pressure of 300 kgf/cm²or more to obtain a sintered compact magnesium oxide target forsputtering having a purity of 99.99 wt % or higher excluding C, and adensity of 3.57 g/cm³ or higher.
 7. The sintered compact magnesium oxidetarget for sputtering according to claim 1, wherein the whiteness is 55%or higher and 60% or less.
 8. The sintered compact magnesium oxidetarget for sputtering according to claim 1, wherein variation in thewhiteness is within 5%.